The involvement of oxygen vacancies in the electronic and structural properties and photocatalytic activity of hydrogenated TiO2 (H-TiO2) for water splitting are currently under debate. Herein, the process for the formation of oxygen vacancies in H-TiO2 is illustrated for the first time to verify the role of these vacancies on the surface and in the bulk of H-TiO2 by using surface-sensitive soft X-ray techniques and bulk-information-included hard X-ray techniques for the O K-edges and Ti K-edges, respectively. We find that oxygen vacancies on the surface and in the bulk contribute differently to tailing of the conduction band of H-TiO2. By controlling the degree of hydrogenation to restrict tailing of the conduction band to just above the H+/H-2 redox potential, the most favorable disordered structure for photocatalytic H-2 evolution is developed. This work promotes a better understanding of the possible negative consequence of hydrogenated semiconductors in H-2 evolution apart from the positive effect on visible-light response.